1. Field of the Invention
The invention relates to a video tape recorder (VTR) with a function of controlling a character display, capable of reproducing a video tape on which a character multiplex signal or teletext signal is recorded.
2. Description of the Related Art
A closed caption system which enables an aurally handicapped viewer to read speeches by means of characters superimposed on a broadcasting screen uses caption information multiplexed in the 21st scanning line of each frame.
In an apparatus for superimpose-displaying such caption information, the caption information is extracted based on a signal indicative of the 21st scanning line in a received video signal. With using a sampling clock signal which is synchronized in phase with a clock run-in signal in the extracted caption information, data codes in the caption information are sampled. Such data codes include character codes indicating characters, and control codes indicating a display control. In order to identify these codes, therefore, the apparatus is provided with a data decoder which decodes data codes. Furthermore, the apparatus is provided with a display signal generator which generates a display signal for a character display synchronized with the scanning timing of a CRT.
When the data decoder identifies a data code as a character code, the character code is written into a video random access memory (RAM) in the display signal generator, and the corresponding character is superimpose-displayed. When a data code is identified as a control code, the display signal generator controls the scroll of the display, the change of display colors, etc. in accordance with the contents of the control code.
Such an apparatus is configured so that, when a video signal in which caption information is not multiplexed is received, the superimpose display is erased, because of the following reason. When no caption information is received, the contents of the video RAM in the display signal generator are not defined. Even when a superimpose display is conducted, therefore, the displayed contents have no meaning.
In some cases, a video tape storing a video signal in which caption information is multiplexed is subjected to a reproduction process, and a superimpose displayed in the reproduction is used in a study of a language. In such cases, if the change of the contents of the superimpose display can be disabled at an arbitrary time, it is very convenient because the superimpose display can be read repeatedly. When the reproduction operation of the video tape is paused in order to disable the change of the contents of a superimpose display, however, the reproduction head cannot correctly reproduce information for one frame, and reproduces information in which information of the target track is mixed with that of an adjacent track or tracks. Consequently, a reproduced signal lacks caption information. Hence, the data decoder judges that caption information is not multiplexed, and instructs the display signal generator to erase a superimpose display. This produces a problem in that, with respect to a superimpose display, the change of the contents of the display cannot be disabled arbitrarily.